possible valve issue

1 reply to this topic
  • joeyz17

Posted July 08, 2013 - 09:35 AM


I looked and couldn't find a similar thread for this issue but may have overlooked it.
I have a 2008 yz450f bought new in 2010.several hours on machine and sporatically acts like it has no compression.
mostly when hot.fires right up and runs smooth,so I check valves and only the center intake valve was off.pulled a180 shim out
and it took a 164 to get it perfect in spec. yet still only sometimes I go to crank ussualy warm after some riding it kicks over a few times
like it has absolutely no compression. I am suspecting a bucket sticking in the head and wondering before I go that far for nothing if anyone
has run into this...thanks

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  • grayracer513

Posted July 08, 2013 - 03:28 PM


It is likely that your temporary compression loss is the result of either worn rings (and/or a piston) or carbon deposits on the valve stem that are preventing the valve from fully seating by jamming the stem in the guide.

It's also unquestionable that the center intake in your engine needs immediate replacement before it drops the valve head on your piston one day.

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